Therapeutically active chloro substituted benzimidazole

ABSTRACT

5-Chloro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole and physiologically acceptable salts thereof as well as an intermediate, pharmaceutical compositions containing such compound as active ingredient, and the use of the compound in medicine.

FIELD OF THE INVENTION

The object of the present invention is to provide a novel compound, andtherapeutically acceptable salts thereof, which inhibit exogenously orendogenously stimulated gastric acid secretion and thus can be used inthe prevention and treatment of peptic ulcer.

The present invention also relates to the use of the compound of theinvention, especially therapeutically acceptable salts thereof, forinhibiting gastric acid secretion in mammals including man. In a moregeneral sense, the compound of the invention may be used for preventionand treatment of gastrointestinal inflammatory diseases, and gastricacid-related diseases in mammals including man, such as gastritis,gastric ulcer, duodenal ulcer, reflux esophagitis, and Zollinger-Ellisonsyndrome. Furthermore, the compound may be used for treatment of othergastrointestinal disorders where gastric antisecretory effect isdesirable e.g. in patients with gastrinomas, and in patients with acuteupper gastrointestinal bleeding. It may also be used in patients inintensive care situations, and pre- and postoperatively to prevent acidaspiration and stress ulceration. The compound of the invention may alsobe used for treatment or prophylaxis of inflammatory conditions inmammals, including man, especially those involving lysozymal enzymes.Conditions that may be specifically mentioned are rheumatoid arthritisand gout. The compound may also be useful in the treatment of diseasesrelated to bone metabolism disorders as well as the treatment ofglaucoma.

The invention also relates to pharmaceutical compositions containing thecompound of the invention, or a therapeutically acceptable salt thereof,as active ingredient. In a further aspect, the invention relates toprocesses for preparation of such new compound, to a novel intermediatein the preparation of the compound and to the use of the active compoundfor the preparation of pharmaceutical compositions for the medical useindicated above.

It is a specific primary object of the invention to provide a compoundwith a high level of bioavailability. The compound of the invention willalso exhibit high stability properties at neutral pH and a high potencyin regard to inhibition of gastric acid secretion. Bioavailability isdefined as the fraction, or percent, of the administered dose ofcompound that is absorbed unchanged into the systemic blood. Potency isin this application defined as the ED₅₀ value.

PRIOR ART AND BACKGROUND OF THE INVENTION

Benzimidazole derivatives intended for inhibiting gastric acid secretionare disclosed in numerous patent documents. Among these can be mentionedGB No. 1 500 043, GB No. 1 525 958, U.S. Pat. Nos. 4 182 766, 4 255 431,4 599 347, 4 555 518, 4 727 150, 4 628 098, EP No. 208 452 and Derwentabstract 87-29449/42. Benzimidazole derivatives proposed for use in thetreatment or prevention of special gastrointestinal inflammatorydiseases are disclosed in U.S. Pat. No. 4 539 465.

THE INVENTION

Compounds described in the prior art, as described above, are effectiveacid secretion inhibitors, and are thus useful as antiulcer compounds.In order to further enhance the usefulness of this type of drugs, ahigher bioavailability has been desired, but still the compounds shouldhave a high potency in inhibiting gastric acid secretion and also a highchemical stability at neutral pH.

It has been recognized that2-[(2-pyridinylmethyl)sulfinyl]-1H-benzimidazoles tested show a greatvariability in bioavailability as well as in potency and stability, andit is difficult to identify compounds possessing all the threeadvantageous properties. There is no guidance in the prior art on how toobtain compounds with this combination of properties.

It has been found that the compound of the invention shows exceedinglyhigh bioavailability, and still the compound is very effective asinhibitor of gastric acid secretion and exhibits a high chemicalstability in solution at a neutral pH. Thus the compound of theinvention can be used in the indications given above in mammalsincluding man.

The compound of the invention is5-chloro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole(compound I) and physiologically acceptable salts thereof having theformula: ##STR1##

The compound of the invention has an asymmetric center in the sulfuratom, i.e. exists as two optical isomers (enantiomers). Both the pureenantiomers, racemic mixtures (50% of each enantiomer) and unequalmixtures of the two are within the scope of the present invention. Alsoone synthetic intermediate compound and process for the preparation arewithin the scope.

Preparation

The compound of the invention, may be prepared according to thefollowing method:

Oxidizing 5-chloro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]thio-1H-benzimidazole (compound II) to give the compound of theinvention. This oxidation may be carried out by using an oxidizing agentsuch as nitric acid, hydrogen peroxide, (optionally in the presence ofvanadium compounds), peracids, peresters, ozone, dinitrogentetraoxide,iodosobenzene, N-halosuccinimide, 1-chlorobenzotriazole,t-butylhypochlorite, diazabicyclo-[2,2,2]-octane bromine complex, sodiummetaperiodate, selenium dioxide, manganese dioxide, chromic acid,cericammonium nitrate, bromine, chlorine, and sulfuryl chloride. Theoxidation usually takes place in a solvent, such as halogenatedhydrocarbons, alcohols, ethers, ketones.

The oxidation may also be carried out enzymatically by using anoxidizing enzyme or microbiotically by using a suitable microorganism.

Depending on the process conditions and the starting materials, thecompound of the invention is obtained either in neutral or salt form.Both the neutral compound and the salts of this are included within thescope of the invention. Thus, basic, neutral or mixed salts may beobtained as well as hemi, mono, sesqui or polyhydrates.

Alkaline salts of the compound of the invention are examplified by itssalts with Li⁺, Na⁺, K⁺, Mg²⁺, Ca^(`+), and N⁺ (R)₄, where R is (1-4C)alkyl. Particularly preferred are the Na⁺, Ca²⁺ and Mg²⁺ salts.Especially preferred are the Na⁺ and Mg²⁺ salts. Such salts may beprepared by reacting the compound with a base capable of releasing thedesired cation.

Examples of bases capable of releasing such cations, and examples ofreaction conditions are given below.

(a) Salts wherein the cation is Li⁺, Na⁺ or K⁺ are prepared by treatingthe compound of the invention with LiOH, NaOH or KOH in an aqueous ornonaqueous medium or with LiOR, LiNH₂, LiNR₂, NaOR, NaNH₂, NaNR₂, KOR,KNH₂ or KNR₂, wherein R is an alkyl group containing 1-4 carbon atoms,in a nonaqueous medium.

(b) Salts wherein the cation is Mg²⁺ or Ca²⁺, are prepared by treatingthe compound of the invention with Mg(OR)₂, Ca(OR)₂ or CaH₂, wherein Ris an alkyl group containing 1-4 carbon atoms, in a nonaqueous solventsuch as an alcohol (only for the alcoholates), e.g. ROH, or in an ethersuch as tetrahydrofuran.

Racemates obtained can be separated into the pure enantiomers. This maybe done according to known methods, e.g. from racemic diastereomericsalts by means of chromatography or fractional crystallization.

The starting materials described in the intermediate examples may beobtained according to processes known per se.

For clinical use the compound of the invention is formulated intopharmaceutical formulations for oral, rectal, parenteral or other modesof administration. The pharmaceutical formulation contains the compoundof the invention normally in combination with a pharmaceuticallyacceptable carrier. The carrier may be in the form of a solid,semi-solid or liquid diluent, or a capsule. These pharmaceuticalpreparations are a further object of the invention. Usually the amountof active compound is between 0.1-95% by weight of the preparation,between 0.2-20% by weight in preparations for parenteral use and between1-50% by weight in preparations for oral administration.

In the preparation of pharmaceutical formulations containing thecompound of the present invention in the form of dosage units for oraladministration the compound selected may be mixed with a solid, powderedcarrier, such as lactose, saccharose, sorbitol, mannitol, starch,amylopectin, cellulose derivatives, gelatin, or another suitablecarrier, stabilizing substances such as alkaline compounds e.g.carbonates, hydroxides and oxides of sodium, potassium, calcium,magnesium and the like as well as with lubricating agents such asmagnesium stearate, calcium stearate, sodium stearyl fumarate andpolyethylenglycol waxes. The mixture is then processed into granules orpressed into tablets. Granules and tablets may be coated with an entericcoating which protects the active compound from acid catalyzeddegradation as long as the dosage form remains in the stomach. Theenteric coating is chosen among pharmaceutically acceptableenteric-coating materials e.g. beeswax, shellac or anionic film-formingpolymers such as cellulose acetate phthalate,hydroxypropyl-methylcellulose phthalate, partly methyl esterifiedmethacrylic acid polymers and the like, if preferred in combination witha suitable plasticizer. To the coating various dyes may be added inorder to distinguish among tablets or granules with different activecompounds or with different amounts of the active compound present.

Soft gelatine capsules may be prepared with capsules containing amixture of the active compound of the invention, vegetable oil, fat, orother suitable vehicle for soft gelatine capsules. Soft gelatinecapsules may also be enteric-coated as described above. Hard gelatinecapsules may contain granules or enteric-coated granules of the activecompound. Hard gelatine capsules may also contain the active compound incombination with a solid powdered carrier such as lactose, saccharose,sorbitol, mannitol, potato starch, amylopectin, cellulose derivatives orgelatine. The hard gelatine capsules may be enteric-coated as describedabove.

Dosage units for rectal administration may be prepared in the form ofsuppositories which contain the active substance mixed with a neutralfat base, or they may be prepared in the form of a gelatine rectalcapsule which contains the active substance in a mixture with avegetable oil, paraffin oil or other suitable vehicle for gelatinerectal capsules, or they may be prepared in the form of a ready-mademicro enema, or they may be prepared in the form of a dry micro enemaformulation to be reconstituted in a suitable solvent just prior toadministration.

Liquid preparation for oral administration may be prepared in the formof syrups or suspensions, e.g. solutions or suspensions containing from0.2% to 20% by weight of the active ingredient and the remainderconsisting of sugar or sugar alcohols and a mixture of ethanol, water,glycerol, propylene glycol and/or polyethylene glycol. If desired, suchliquid preparations may contain colouring agents, flavouring agents,saccharine and carboxymethyl cellulose or other thickening agents.Liquid preparations for oral administration may also be prepared in theform of a dry powder to be reconstituted with a suitable solvent priorto use.

Solutions for parenteral administration may be prepared as a solution ofthe compound of the invention in a pharmaceutically acceptable solvent,preferably in a concentration from 0.1% to 10% by weight. Thesesolutions may also contain stabilizing agents and/or buffering agentsand may be manufactured in different unit dose ampoules or vials.Solutions for parenteral administration may also be prepared as a drypreparation to be reconstituted with a suitable solvent extemporaneouslybefore use.

The typical daily dose of the active substance will depend on variousfactors such as for example the individual requirement of each patient,the route of administration and the disease. In general, oral andparenteral dosages will be in the range of 5 to 500 mg per day of activesubstance.

The invention is illustrated by the following examples.

EXAMPLE 1 Preparation of5-chloro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole

5-chloro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]thio]-1H-benzimidazole(645 mg, 0.0019 mol) was dissolved in 25 ml CH₂ Cl₂ and mixed withNaHCO₃ (323 mg, 0.0038 mol) dissolved in 10 ml H₂ O. The stirred mixturewas cooled to 0° C. and treated with MCPBA (84%, 389 mg, 0.0019 mol)dissolved in 6 ml CH₂ Cl₂. After reacting for 10 min the layers wereseparted and the aqueous layer extracted with 5 ml CH₂ Cl₂. The organiclayers wcre combined and extracted with 20 ml water containing NaOH (154mg, 0.0038 mol). The latter aqueous layer was collected (residual CH₂Cl₂ distilled off on the rotavapor) and treated with two portions ofHCOOCH₃ (2×118 μl, 0.0038 mol).

The solid thus formed was collected, washed with a small volume of icecold water leaving 253 mg (38%) pure product as a white powder. Themother liquor was quickly extracted with 20+10 ml CH₂ Cl₂. The organiclayers were combined, dried over MgSO₄, and evaporated leaving a foamwhich upon treatment with CH₃ CN spontaneously crystallized. The solidwas collected, washed with a small volume of ice cold CH₃ CN affordingadditional 225 mg (34%) pure title compound. NMR data is given below.

EXAMPLE 2 Preparation of5-chloro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole,sodium salt

5-chloro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole(4.1 g; 11.65 mmol) dissolved in dichloromethane (100 ml) and sodiumhydroxide (0.46 g; 11.5 mmol) dissolved in water (100 ml) weretransferred to a separatory funnel. The mixture was shaken toequilibrium whereupon the solvent phases were separated. The watersolution was washed with dichloromethane (2×25 ml) and then freezedried. The residue was recrystallized from ethyl acetate/diethyl ether.

Yield: 3.7 g (86 %) of the title compound. NMR data is given below.

                  TABLE 1                                                         ______________________________________                                        Ex. Solvent  NMR data δ ppm                                             ______________________________________                                        1 CDCl.sub.3 3.84(s, 3H), 3.88(s, 3H), 4.70(d, 1H),                           (500 MHz)    4.84(d, 1H), 6.80(d, 1H), 7.26(dd, 1H),                                       7.55(d, 1H), 7.58(d, 1H), 8.16(d, 1H),                           2 D.sub.2 O δ(D.sub.2 O 4.82)                                                        3.69(s, 3H), 3.91(s, 3H), 4.64(d, 1H),                           (300 MHz)    4.80(d, 1H), 7.04(d, 1H), 7.20(m, 1H),                                        7.60(d, 1H), 7.67(d, 1H), 8.11(d, 1H)                            ______________________________________                                    

Preparation of synthetic intermediates Example I 1. Preparation of3,4-dimethoxy-2-chloromethylpyridine.

3,4-Dimethoxy-2-hydroxymethylpyridine (0.34 g, 0.002 mol) was dissolvedin CH₂ Cl₂ (8 ml). SOCl₂ (0.27 g, 0.00227 mol) in CH₂ Cl₂ (2 ml) wasadded under stirring at room temperature. After 10 min the mixture wasneutralized with NaHCO₃ (5 ml). The phases were separated, the CH₂ Cl₂phase was washed with NaCl-solution, dried over Na₂ SO₄ and evaporatedgiving the desired product (0.61 g, 88%).

Example I 2 Preparation of5-chloro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]thio]-1H-benzimidazole

2-chloromethyl-3,4-dimethoxypyridine hydrochloride (896 mg, 0.004 mol)was dissolved in 25 ml MeOH and treated with NaOH (390 mg, 0.008 mol)dissolved in 1.5 ml H₂ O. 5-chloro-2-mercapto-1H-benzimidazole (812 mg,0.0044 mol) was added and the resulting mixture allowed to react for 2hat room temperature. The solvent was evaporated and the residuepartitioned between 50 ml 2.5 % NaOH and 75 ml CH₂ Cl₂. The aqueouslayer was separated and extracted twice with 25 ml CH₂ Cl₂. The organiclayers were combined, washed with 25 ml H₂ O, dried over MgSO₄ and thesolvent was evaporated.

The crude product was triturated with approximately 5 ml of EtOAcsaturated with NH₃. The solid was collected and the mother liquorreprocessed furnishing 650 mg (48%) of the title compound as an offwhite powder.

Identifying data for the starting compound according to the example aregiven in Table 2.

                  TABLE 2                                                         ______________________________________                                        Ex.    Solvent    NMR data δ ppm (500 MHz)                              ______________________________________                                        I-2    CD.sub.2 Cl.sub.2                                                                        3.96(s, 3H), 3.99(s, 3H), 4.46(s, 2H),                                        6.96(d, 1H), 7.18(dd, 1H),                                                    7.48(d, 1H), 7.56(d, 1H), 8.31(d, 1H).                      ______________________________________                                    

The best mode of carrying out the invention known at present is to usethe sodium salt of the compound of the formula I, thus the compounddescribed in Example 2.

Pharmaceutical preparations containing the compound of the invention asactive ingredient are illustrated in the following formulations.

Syrup

A syrup containing 1% (weight per volume) of active substance wasprepared from the following ingredients:

    ______________________________________                                        Compound according to Example 1                                                                         1.0    g                                            Sugar, powder             30.0   g                                            Saccharine                0.6    g                                            Glycerol                  5.0    g                                            Flavouring agent          0.05   g                                            Ethanol 96%               5.0    g                                            Distilled water q.s. to a final volume of                                                               100    ml                                           ______________________________________                                    

Sugar and saccharine were dissolved in 60 g of warm water. After coolingthe active compound was added to the sugar solution and glycerol and asolution of flavouring agents dissolved in ethanol were added. Themixture was diluted with water to a final volume of 100 ml.

Enteric-coated tablets

An enteric coated tablet containing 50 mg of active compound wereprepared from the following ingredients:

    ______________________________________                                        I     Compound according to Example 1                                                                       500    g                                              as Mg salt                                                                    Lactose                 700    g                                              Methyl cellulose        6      g                                              Polyvinylpyrrolidone cross-linked                                                                     50     g                                              Magnesium stearate      15     g                                              Sodium carbonate        6      g                                              Distilled water         q.s.                                            II    Cellulose acetate phthalate                                                                           200    g                                              Cetyl alcohol           15     g                                              Isopropanol             2000   g                                              Methylene chloride      2000   g                                        ______________________________________                                    

I Compound according to example 1, powder, was mixed with lactose andgranulated with a water solution of methyl cellulose and sodiumcarbonate. The wet mass was forced through a sieve and the granulatedried in an oven. After drying the granulate was mixed withpolyvinylpyrrolidone and magnesium stearate. The dry mixture was pressedinto tablet cores (10 000 tablets), each tablet containing 50 mg ofactive substance, in a tabletting machine using 7 mm diameter punches.

II A solution of cellulose acetate phthalate and cetyl alcohol inisopropanol/methylene chloride was sprayed onto the tablets I in anAccela Cota®, Manesty coating equipment. A final tablet weight of 110 mgwas obtained.

Solution for intravenous administration

A parenteral formulation for intravenous use, containing 4 mg of activecompound per ml, was prepared from the following ingredients:

    ______________________________________                                        Compound according to Example 2                                                                        4      g                                             Sterile water to a final volume of                                                                     1000   ml                                            ______________________________________                                    

The active compound was dissolved in water to a final volume of 1000 ml.The solution was filtered through a 0.22 μm filter and immediatelydispensed into 10 ml sterile ampoules. The ampoules were sealed.

Capsules

Capsules containing 30 mg of active compound were prepared from thefollowing ingredients:

    ______________________________________                                        Compound according to Example 1                                                                         300    g                                            Lactose                   700    g                                            Microcrystalline cellulose                                                                              40     g                                            Hydroxypropyl cellulose low-substituted                                                                 62     g                                            Disodium hydrogen phosphate                                                                             2      g                                            Purified water            q.s.                                                ______________________________________                                    

The active compound was mixed with the dry ingredients and granulatedwith a solution of disodium hydrogen phosphate. The wet mass was forcedthrough an extruder and spheronized and dried in a fluidized bed dryer.

500 g of the pellets above were first coated with a solution ofhydroxypropyl methylcellulose, 30 g, in water, 750 g, using a fluidizedbed coater. After drying, the pellets were coated with a second coatingas given below:

    ______________________________________                                        Coating solution:                                                             ______________________________________                                        Hydroxypropyl methylcellulose phthalate                                                                  70 g                                               Cetyl alcohol              4 g                                                Acetone                    200 g                                              Ethanol                    600 g                                              ______________________________________                                    

The final coated pellets were filled into capsules.

Suppositories

Suppositories were prepared from the following ingredients using awelding procedure. Each suppository contained 40 mg of active compound.

    ______________________________________                                        Compound according to Example 1                                                                         4 g                                                 Witepsol H-15             180 g                                               ______________________________________                                    

The active compound was homogenously mixed with Witepsol H-15 at atemperature of 41° C. The molten mass was volume filled intopre-fabricated suppository packages to a net weight of 1.84 g. Aftercooling the packages were heat sealed. Each suppository contained 40 mgof active compound.

BIOLOGICAL EFFECTS Bioavailability Choice of Species for Testing.

The results from tests on two different animal species, rat and dog,vary in regard to measured level of bioavailability for the samecompound. We believe that the rat is the more relevant species forbioavailability testing. This is based on our belief that livermetabolism has the most predominant impact upon bioavailability, andthat the liver metabolic pattern in man for this type of compounds isquite similar to that of the male rat (more so than of the female ratand the dog). Moreover, test results of bioavailability in the male ratwill tend to give a broader "spread" compared with the test results inthe dog, and thus the male rat model will give more clear differences inbioavailability between different compounds. Stated in another way, thebioavailability as tested in the male rat can be expected to give abetter estimate of the relative differences in man between differenttest compounds compared with the test results obtained when using thesame compounds in the dog.

Assessment of Bioavailability.

Bioavailability is assessed by calculating the quotient between the areaunder plasma concentration (AUC) curve following intraduodenal (id)administration and intravenous (iv) administration from the rat or thedog. Low, therapeutically relevant doses, were used. This method isscientifically recognized as valid for assessing bioavailability (seefor instance: M. Rowland and T.N. Tozer, Clinical Pharmacokinetics, 2nded., Lea & Febiger, London 1989, p 42). The data from both the rat andthe dog are provided in Table 3.

Rough Screening Model.

Since the bioavailability model described above is time and labourintensive, and requires a large number of plasma analyses, also a roughscreening model, based on relative potencies to inhibit acid secretion,has been used (see for instance: A. Goth, Medical Pharmacology, 7th ed.,C. V. Mosby Company, Saint Louis 1974, p 19). Thus, the ratio (called"Bioavailability" in Table 3) between the ED₅₀ at intravenousadministration and the ED₅₀ at intraduodenal administration wascalculated. Also these data are provided in Table 3.

Potency

The potency for inhibition of acid secretion has been measured in themale rat and the dog, both intravenously and intraduodenally. When itcomes to relevance of the animal test data for potency of a givencompound in man for the present type of compounds, it is believed thatpotency in man will correspond to a level somewhere between what ismeasured in the male rat and what is measured in the dog. Potency datafrom the two animal species are given in Table 3.

Biological Tests

Inhibition of Gastric Acid Secretion in the Conscious Male Rat.

Male rats of the Sprague-Dawley strain were used. They were equippedwith cannulated fistulae in the stomach (lumen) and the upper part ofthe duodenum, for collection of gastric secretions and administration oftest substances, respectively. A fourteen days recovery period aftersurgery was allowed before testing commenced.

Before secretory tests, the animals were deprived of food but not waterfor 20 h. The stomach was repeatedly washed through the gastric cannula,and 6 ml of Ringer-Glucose given s.c. Acid secretion was stimulated witha infusion during 3.5 h (1.2 ml/h, s.c.) of pentagastrin and carbachol(20 and 110 nmol/kg h, respectively), during which time gastricsecretions were collected in 30-min fractions. Test substances orvehicle were given iv or id at 90 min after starting the stimulation, ina volume of 1 ml/kg. Gastric juice samples were titrated to pH 7.0 withNaOH, 0.1 mol/L, and acid output calculated as the product of titrantvolume and concentration. Further calculations were based on group meanresponses from 4-5 rats. The acid output during the periods afteradministration of test substances or vehicle were expressed asfractional responses, setting the acid output in the 30-min periodpreceding administration to 1.0. Percentage inhibition was calculatedfrom the fractional responses elicited by test compound and vehicle.ED₅₀ values were obtained from graphical interpolation on logdose-response curves, or estimated from single-dose experiments assuminga similar slope for all dose-response curves. An estimation of thebioavailability was obtained by calculating the ratio ED₅₀ iv /ED₅₀ id.The results reported are based on gastric acid secretion during thesecond hour after drug/vehicle administration.

Bioavailability in the Male Rat.

Male adult rats of the Sprague-Dawley strain were used. One day, priorto the experiments, all rats were prepared by cannulation of the leftcarotid artery under anaesthesia. The rats used for the intravenousexperiments, were also cannulated in the jugular vein. (Ref. V Popovicand P Popovic, J Appl Physiol 1960;15,727-728). The rats used for theintraduodenal experiments, were also cannulated in the upper part of theduodenum. The cannulas were exteriorized at the nape of the neck. Therats were housed individually after surgery and were deprived of food,but not water, before administration of the test substances. The samedose (4 μmol/kg) were given iv and id as a bolus for about: one minute(2 ml/kg).

Blood samples (0.1-0.4 g) were drawn repeatedly from the carotid arteryat intervals up to 4 hours after given dose. The samples were frozen assoon as possible until analysis of the test compound.

The area under the blood concentration vs time curve, AUC, wasdetermined by the linear trapezoidal rule and extrapolated to infinityby dividing the last determined blood concentration by the eliminationrate constant in the terminal phase. The systemic bioavailability (F %)following intraduodenal administration was calculated as ##EQU1##

Inhibition of Gastric Acid Secretion and Bioavailability in theConscious Dog.

Harrier dogs of either sex were used. They were equipped with a duodenalfistula for the administration of test compounds or vehicle and acannulated ventricular fistula for the collection of gastric secretions.

Before secretory tests the animals were fasted for about 18 h but waterwas freely allowed. Gastric acid secretion was stimulated by a 4 hinfusion of histamine dihydrochloride (12 ml/h) at a dose producingabout 80% of the individual maximal secretory response, and gastricjuice collected in consecutive 30-min fractions. Test substance orvehicle was given id or iv 1 h after starting the histamine infusion, ina volume of 0.5 ml/kg body weight. The acidity of the gastric juicesamples were determined by titration to pH 7.0, and the acid outputcalculated. The acid output in the collection periods afteradministration of test substance or vehicle were expressed as fractionalresponses, setting the acid output in the fraction precedingadministration to 1.0. Percentage inhibition was calculated fromfractional responses elicited by test compound and vehicle. ED₅₀--values were obtained by graphical interpolation on log dose-responsecurves, or estimated from single-dose experiments under the assumptionof the same slope of the dose-response curve for all test compounds. Allresults reported are based on acid output 2 h after dosing.

Blood samples for the analysis of test compound concentration in plasmawere taken at intervals up to 3 h after dosing. Plasma was separated andfrozen within 30 min after collection. AUC (area under the plasmaconcentration--time curve), extrapolated to infinite time, wascalculated by the linear trapezoidal rule. The systemic bioavailability(F %) after id administration was calculated as 100×(AUC_(id)/AUC_(iv)).

Chemical Stability

The chemical stability of various compounds of the invention has beenfollowed kinetically at low concentration at 37° C. in aqueous buffersolution at different pH values. The results in Table 3 show the halflife (t 1/2) at pH 7, that is the time period after which half theamount of the original compound remains unchanged.

Results of biological and stability tests

Table 3 gives a summary of the test data available for the compound ofthe invention and a structurally closely related compound genericallydisclosed in the prior art, called Ref. in Table 3, namely5-fluoro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazolewithin the scope of EP 208 452. As can be seen from Table 3 the compoundaccording to the invention has a high bioavailability (F=97% in therat), high potency (ED₅₀ iv=1.3 μmol/kg, ED₅₀ id=2.6 μmol/kg in the rat)and high chemical stability (t 1/2=30 h). The bioavailability of thecompound of the invention has a much higher value (97% vs 47%) comparedto that of the Ref. compound, although the Ref. compound has higherpotency and stability. (ED₅₀ iv=0.85 μmol/kg, ED₅₀ id=1.75 μmol/kg and t1/2=58 h for the Ref compound).

                                      TABLE 3                                     __________________________________________________________________________    Biological Test Data and Stability Data                                               Inhibition of                                                                 acid secretion              Bioavailability                                                                        Chemical                                 Dog ED.sub.50                                                                         Rat, ED.sub.50                                                                        "Bioavailability"                                                                         measured by the                                                                        Stability at                             (μmol/kg)                                                                          (μmol/kg)                                                                          measured by the Rough                                                                     AUL-method                                                                             pH 7                             Test compound                                                                         Route of adm.                                                                         Route of adm.                                                                         Screening Model                                                                           F %      half-life                        Example no.                                                                           iv  id  iv  id  Rat ED.sub.50 iv/ED.sub.50 id (%)                                                         Dog  Rat (t 1/2) h                        __________________________________________________________________________    1       1.75.sup.2                                                                        1.2 1.3 2.6 50          n.t. 97  30                               Ref.    n.t.                                                                              .sup. 1.1.sup.1                                                                    0.85                                                                              1.75                                                                             49          n.t. 47  58                               __________________________________________________________________________     n.t. = not tested                                                             .sup.1 Dog 1 1.0 μmol/kg gave no effect                                    Dog 2 2.0 μmol/kg gave 70% inhibition                                      ED.sub.50 value was estimated from one dog.                                   .sup.2 Only one dog                                                      

We claim: 1.5-Chloro-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazoleand physiologically acceptable salts thereof, as well as its opticalenantiomers.
 2. A compound according to claim 1 in the form of itssodium salt.
 3. A compound according to claim 1 in the form of itsmagnesium salt.
 4. A pharmaceutical composition containing as activeingredient an effective amount of a compound according to claim
 1. 5. Amethod for inhibiting gastric acid secretion by administering to mammalsan amount of a compound as defined in claim 1 effective to inhibitgastric acid secretion.
 6. A method for the treatment ofgastrointestinal inflammatory diseases in mammals by administering anamount of a compound as defined in claim 1 effective to inhibit gastricacid secretion. 7.5-Chloro-2[[(3,4-dimethoxy-2-pyridinyl)methyl]thio-1H-benzimidazole.